In the conventional techniques of overrunning clutches, two kinds of overrunning clutches are most widely used, which include a roller type overrunning clutch and a wedge type overrunning clutch which both employ a principle using inclined surfaces for wedge joint. The above two kinds of overrunning clutches mainly have the following defects. 1. All the contacts are discrete higher pair contacts, and the contact stress is very high in a wedged state, resulting in a very small bearing capacity, thus the contact pair wears fast, and has a short service life. 2. Since the discrete contact pair is used, a situation that discrete members cannot operate synchronously is apt to occur, which is extremely apt to cause partial damages that will in turn cause failures or malfunctions of dead lock or failing in self-lock. 3. There is nearly no automatic wear compensation capacity. 4. In an overrunning state, the resistance is large, and the efficiency is not high. 5. A great releasing force is required for removing the wedged connection. 6. The slipping angle is large. 7. The structure is complex and has a large number of parts, which imposes very high consistency requirements on both materials and manufacture process, thus the cost is high. 8. Due to the large number of discrete members, at a high rotational speed, the working performance is poor, especially in a high rotational speed overrunning state, both noise and abrasion are large.
The above defects in the conventional technology seriously impact the scope of application of the overrunning clutch. Reference is made to an article of “The Status and Trend of Development of Overrunning Clutch” written by Zhang Jizheng, and et al. (which is published in collection of the third China-Japan International Academic Conference on History of Mechanical Technology on Oct. 28, 2002, the publisher of which is Chinese mechanical engineering society). It may be learnt from the contents of the article that, the domestic scholars and experts have made lots of improvements and researches and inventions, and have made good achievements, but there is still a big gap to achieve requirements of the overrunning clutch such as ideal performance, structure, reliability, cost and service life.
Document CN2175321Y discloses a one-way clutch based on screw thread pair and conical surface friction pair, however, did not disclose the condition for realizing self-lock.
Document CN2479288Y discloses a one-way overrunning clutch based on inclined slot shaft pin and conical surface friction pair, and in addition to the drawbacks similar to those of the document CN2175321Y, the clutch has a defect of low bearing capacity.
Documents CN201747821 U and CN 101936346 A disclose a spatial wedge joint type friction overrunning clutch, and as described in the documents, “it is designed on basis of a novel technology principle”, however, in one aspect, “the novel technology principle” is not clarified in the document; and in another aspect, the clutch according to these two documents selects a structure using a friction pair of a guide mechanism to realize self-lock, which greatly limits the improvements of the structure design, the unlocking performance and bearing capacity of the overrunning clutch.